A nuclear fuel assembly for boiling water reactor (BWR) conventionally comprises a bundle of fuel rods and at least one tubular water channel encased in a tubular fuel channel. Each water channel replaces at least one fuel rod in the bundle.
Each fuel rod comprises a tubular cladding receiving a stack of nuclear fuel pellets and closed at its ends by end plugs.
The fuel assembly comprises a plurality of spacer grids distributed along the fuel assembly for maintaining the fuel rods transversely in spaced relationship. Each spacer grid comprises guide cells through each of which a fuel rod usually extends.
The fuel assembly comprises an upper nozzle at the upper end of the fuel channel and a lower nozzle at the lower end of the fuel channel. Fuel rods extend from the upper nozzle to the lower nozzle. Each nozzle has guide cells each for receiving a respective fuel rod end plug and channels for allowing coolant to flow through the nozzle.
In operation, the fuel assembly is oriented vertically in a nuclear reactor core and a coolant is caused to flow upwardly between the fuel rods. The coolant flows in the water channel and the fuel channel, from lower end to upper end of the fuel assembly. Coolant enters the fuel channel through the lower nozzle and exits the fuel channel through the upper nozzle.